In Long Term Evolution (LTE) Release8/9 (R8/9), a Common Reference Signal (CRS) is designed for channel quality measurement and demodulation of a received data symbol. A terminal or User Equipment (UE) may perform channel measurement through a CRS, thereby making a cell reselection decision and switching to a taget cell. Channel quality measurement is performed while the UE is connected. When there is a high level of interference, physical-layer disconnection may be implemented through relevant higher-layer radio link failure signaling. In LTE R10, to further increase cell average spectrum utilization, cell edge spectrum utilization, and UE throughput, two reference signals are defined respective, namely, a Channel State Information-Reference Signal (CSI-RS) and a DeModulation Reference Signal (DMRS). The CSI-RS is used for channel measurement. A Precoding Matrix Indicator (PMI), a Channel Quality Indicator (CQI) and a Rank Indicator (RI) to be fed by a UE back to an eNB may be computed through CSI-RS measurement. The DMRS is used for downlink shared channel demodulation. Demodulation with the DMRS not only may reduce interference between different receiving sides and between different cells by way of a beam, but also may reduce performance degradation caused by codebook granularity, as well as reducing downlink control signaling overhead to some extent, as no PMI bit overhead has to be added in a Physical Downlink Control Channel (PDCCH).
In LTE R8, R9 and R10, a PDCCH mainly may be distributed over first 1, 2, or 3 Orthogonal Frequency Division Multiplexing (OFDM) symbols of a subframe. A specific distribution is to be configured in accordance with a subframe type and a CRS port number, as shown in Table 1.
TABLE 1number of OFDMnumber of OFDMsymbols forsymbols forPDCCH withPDCCH withsubframeNRBDL > 10NRBDL ≦ 10subframe 1 and subframe 6 in1, 22subframe type 2MBSFN subframe on a1, 22PDSCH supporting carrier, with aCRS port number of 1 or 2MBSFN subframe on a22PDSCH supporting carrier, with aCRS port number of 4subframe on a carrier00supporting no PDSCH transferPRS non-MBSFN subframe1, 2, 32, 3(other than subframe 6 of framestructure type 2)subframe of any other situation1, 2, 32, 3, 4
A receiving side has to perform blind detection over the first three symbols. A starting position of the blind detection and a control channel element number may depend on a Radio Network Temporary Identitfier allocated to the receiving side as well as control information. In general the control information may include public control information and dedicated control information. The public control information is in general placed in a common search space of a PDCCH. The dedicated control may be placed in a common space and a dedicated search space. After blind detection, a receiving side may determine whether there is any common system message, downlink scheduling information, or uplink scheduling information in a subframe. As such downlink control information has no Hybrid Automatic Repeat Request (HARQ) feedback, a symbol error rate in detection as low as possible has to be ensured.
in an LTE R10 heterogeneous network, there is strong mutual interference between eNBs of different types. Given interference of a Macro eNodeB to a Pico and interference of a Home eNodeB to a Macro eNodeB, it is proposed to handle mutual interference between eNBs of different types by resource muting, specifically based on a subframe such as an Almost Blank Subframe (ABS), or based on a resource element, such as by CRS muting.
the muting method not only adds to resource waste, but also greatly limit scheduling. In particular, given ABS configuration of a Macro eNodeB, more Picos and more ABSs configured for the Macro eNodeB will bring greater impact on the Macro eNodeB, adding to resource waste as well as increasing a scheduling delay. Although interference among control channel data resources may be reduce with a control channel in an ABS, interference between a CRS resource and a data resource cannot be solved. The CRS muting fails to handle interference among data resources, and leads to poor backward compatibility, adding to an access delay and standardization effort.
In LTE R11, more users may be introduced to perform sending on a Multicast Broadcast Single Frequency Network (MBSFN) subframe, which may result in insufficient PDCCH capacity of 2 OFDM symbols configured for the MBSFN. To ensure backward compatibility with an R8/R9/R10 user, a new control information transmission resource (ePDCCH for short hereinafter) has to be created with a Physical Downlink Shared Channel (PDSCH) resource. With COMP introduced in R11, it is possible to handle interference between cells of different types by space division, save resource overhead, avoid resource waste caused by muting, and reduce the limit on scheduling. However, such a solution by space division cannot be implemented with a time-domain PDCCH at present. Such a time-domain PDCCH has to be kept for backward compatibility with R8 and R9. In this case, in order to handle interference between control channels by space division, a new control channel, namely, an Enhanced PDCCH (ePDCCH) has to be introduced. With the ePDCCH, good space division may be implemented, reducing physical downlink control signaling interference between different nodes and increasing system PDCCH capacity.
Also discussed in R11 is Physical Hybird ARQ Indicator Channel (PHICH) resource insufficiency. In R11, more uplink users has to be supported. In particular, in scene 4, a number of supportable uplink users increases significantly, PHICH capacity is limited greatly. In addition, R11 discussion supports different UEs to have identical uplink time-frequency resources/cyclic displacement allocation/CSHopping allocation/different Reference Signal (RS) sequences. Thus, conventional PHICH detecting resource allocation no longer applies, and further PHICH enhancement is required. Thus, further study on PHICH enhancement is necessary. Such an enhanced PHICH may be referred to as an Enhanced Physical Hybird ARQ Indicator Channel (ePHICH).
Also discussed in an R11 conference at present is whether common search space control signaling enhancement is required, which mainly depends on whether an R10 common search space at present has limited capacity and how severe is interference between different nodes, in particular Macro (Macro cell)-Pico (Pico cell) interference. With limited capacity or severe interference, it is necessary to introduce an enhanced common search space. As interference avoidance at a time-frequency resource position may be performed in a PDSCH area, a focus at present is an enhanced common search space based on a PDSCH area, referred to as an Enhanced Common Search Space (eCSS).
In discussion of the latest seventieth 3GPP conference, a preliminary conclusion is formed as follows.
An ePDCCH detecting cluster may consist of N Physical Resource Block (PRB) pairs.
The N may be 1 (N=1, localized ePDCCH transmission mode), 2, 4, 8, 16 (distributed ePDCCH transmission mode).
In the distributed ePDCCH transmission mode, an ePDCCH performs transmission using N PRB pairs in an ePDCCH detecting cluster.
In the localized ePDCCH transmission mode, transmission is performed in an ePDCCH detecting cluster. Further discussion is required to decide whether to support transmission on more than one PRB pair in the localized ePDCCH transmission mode.
K ePDCCH clusters (K≧1) may be configured by UE dedicated higher-layer signaling.
A maximal value of K may be 2, 3, 4 or 6.
An N may be configured for each of the K clusters.
A total number of blind detections for each of the K clusters is independent.
A total number of blind detections for a UE should be allocated to the K clusters.
An ePDCCH detecting cluster is configured to be in either the localized ePDCCH transmission mode or the distributed ePDCCH transmission mode.
PRB pairs of two logic ePDCCH detecting clusters may coincide with each other or partly overlap with each other, or have no overlap at all.